how to use a MBC

[LMKVICDSM]

i totally forgot how to use an MBC, i've read around and they say different things and so now im just confused.

was it screw out for less psi, and screw in for more psi? or vice versa let me know so i can lower the boost on my 2g gsx, thanks.

 

[All_Boost16G]

Out less PSI, In more PSI

 

[95'RS-T]

Mine is IN LESS, OUT MORE

 

[Calan]

Depends on the MBC, but with the common ball and spring type as you turn CW you are compressing the spring which causes more pressure to be needed to overcome it. Once the pressure overcomes the spring, it escapes past the ball and to the atmosphere. Increasing spring pressure has the effect of raising your boost.

So normally, turning CW raises the boost and CCW lowers it.

You can set it to a "start" point by blowing into the inlet and adjusting it until you feel it getting harder to blow through. Otherwise, you may be cranking it down for a while and nothing will happen...if it's been backed out too far.

 

[LMKVICDSM]

thanks for the replies, is there a way to tell if your actually lowering boost without driving the car?

 

[neoviper]

Yes. As calan stated if you have a ball and spring type mbc than turning clockwise would increase boost since you're compressing the spring. Use the method he stated by blowing in through the end of the mbc. when air starts to leak through than the direction you were turning your mbc is lowering the boost.

 

[infinite_kaos]

There's a way to test it with a boost leak tester, the waste gate should open at whatever you have the boost controller set at.

To test which way is more and which is less psi, you can tke the mbc out, blow through one end while turning the knob, you'll feel it get less or more restricted.

 

[Calan]

the waste gate should open at whatever you have the boost controller set at.

Ummm... not really.

You'd think so, but in fact the boost controller reacts dynamically. For one thing, you have a varying amount of resistance being caused by exhaust flow against the wastegate flapper which must be taken into account, along with different flapper surface areas, different vac line diameters/lengths, exhaust backpressure, turbine efficiency, amount that the flapper opens, etc. etc. (Incidently, some of these same factors are why one person's car will have crazy boost creep and a similar car won't).

You can use an air compressor and a decent low pressure gauge to get in the ball park (maybe...depending on your setup), but it will not be the true amount of pressure required to balance the system at some desired boost level. The true amount of pressure in the MBC line needed to overcome the return spring and open the wastegate will be a result of the combination of many factors.